This invention relates to a circuit arrangement for a charge status indicator of a primary battery or a secondary battery (rechargeable accumulator) in an electrical appliance as, for example, a battery-powered shaving apparatus.
Voltage-dependent battery monitoring devices are known in the art which detect the charge status of the battery during operation of the appliance in one or several stages, indicating the charge status permanently or intermittently and/or providing an information of a specified charge status after the appliance is turned off.
Indicating devices which indicate the charge status permanently in several stages after the appliance is turned off require high technical complexity (microcontroller) and are accordingly expensive. On the other hand, inexpensive indicators draw such a high current that a permanent indication after the appliance is turned off is possible for only a short period because its drain on the battery.
Further, from the journal EDN--Electrical Design News, Vol. 35 (1990), Aug. 20, No. 17, Newton, Mass., US, page 151, an indicating device is known in which the battery voltage is applied to a voltage divider, and a voltage tapped in this voltage divider is fed to a microcontroller input. This microcontroller receives further voltage values to provide a comparator with a hysteresis, as well as an external oscillation frequency intended to operate, where applicable, a light-emitting diode serving as an indicating device. This indicating device is rendered active when the battery voltage has dropped to a critical value. In this prior art, the power consumption of the indicating device is lowered by operating the indicating device intermittently with the external oscillation frequency.
It is an object of the present invention to provide a circuit arrangement for a charge status indicator which is of a straightforward and inexpensive construction and draws such a low current that its connection to the battery can be always maintained also after the appliance is turned off.